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15

I am confused, can evolution ( speciation ) really occur in such a short time? Well, Evolution and Speciation are not the same. Evolution is the adaptation of an existing species to an environment over generations. Speciation is the development of a new species, and the definition of "species" can vary depending on who you talk to - but a very commonly ...


10

Rice and Salt$^1$ bred fruit flies for 35 generations and from one line of flies created two groups that were isolated from each other reproductively. They could not interbreed because they no longer bred in the same environment. Depending on one's definition of 'species' this could be a case of artificial speciation. $^1$Rice WR, Salt GW (1988), Speciation ...


8

This is a common misconception about evolution, many skeptics ask something along the lines of "If humans evolved from monkeys, why are there still monkeys?" The answer is that evolution is not a linear process of one species becoming the next species becoming the next. Species branch off much more like a tree. At some point in the past the last common ...


8

Evolution can occur in just one full generation Strong selection will rapidly reduce the gene frequencies of genes which cause negatively selected phenotypes. This reduces the likelihood of unfavourable genotypes occurring in the next generation. (I regard generation here as the complete cycle of one individual being born to the point at which they ...


7

Well, what you seem to be suggesting is "Did life evolve twice on Earth?" Your original question has an answer: Probably yes. It's not unlikely to think that the original cell evolved into two different paths and then one went extinct. However, that doesn't address LUCA. If we found fossil evidence of what we thought was LUCA, and then fossil evidence that ...


5

A commonly used empirical example of species selection (a.k.a clade selection, lineage selection) is pelagic larvae in sessile ocean species. See Maliska et al (2013) for a recent paper discussing this in Tunicata and Jablonski & Hunt (2006) for larval modes in gastropods. The idea is to some extent really intuitive - pelagic larvae means higher ...


5

How are such species are defined, and at what point dogs stop being dogs anymore? This is a bit like the is-Pluto-a-planet-discussion. A group of scientists have to come together and hold a big conference. You have a few principles that you want to adhere to and then it's big groups of people making decisions.


4

You are mixing up two different things in your question: the mechanisms (processes) that cause micro- and macroevolution, and the genetic basis for different types of traits. The processes of evolution (selection & drift acting on genetic variation) are the same for both micro- and macroevolution, and this what the Wikipedia article is stating. ...


4

We can be reasonably certain that ALL species that exist today share a common ancestor, a common origin. Every single species we have even encountered, for example, uses a long chain of nucleotides (DNA or RNA1) to store its genetic information. If life had arisen through multiple independent sources, we would expect to find different solutions to the ...


4

Diane Dodd's experiments on Drosophila pseudoobscura would be another example of lab-based speciation. http://www.jstor.org/stable/2409365?__redirected To summarise - four populations each adapted to feeding on a starch-based diet and a maltose-based diet were evolved in the lab to test effects on mating preferences; compared to what is expected by ...


3

I understand heterozygote inferiority (also underdominance or heterozygote disadvantage) as the opposite of heterozygote advantage, that is, lower fitness of the heterozygous genotype than either homozygote (as reference, see Hedrick, 2009, p. 119). I haven't seen the term structural underdominance before. However, heterozygote disadvantage can sometimes be ...


3

Such examples are not that rare: multiple species are polymorphic for supernumerary (B-chromosomes), others are known to show intra-specific Robertsonian polymorphism (fusions of acrocentric/separation of metacentric chromosomes). One very well studied example, which covers both intra- and inter-specific crossings, are isopod crustaceans from the Jaera ...


3

Cats, dogs and bears all belong to the Carnivora clade of mammals, but they are not the only ones belonging to this clade. For instance, cats are more closely related to mongoose and hyenas than to dogs or bears, who in turn are more closely related to raccoons, weasels, and walruses. Their common ancestors likely displayed various adaptations to a ...


3

There are many definitions of a species, which may or may not include the concept of reproductive barrier. The Biological Species Concept (BSC) is quite popular and involves a reproductive barrier, but other concepts such as the Phylogenetic Species Concept do not include a reproductive barrier. Disagreements and confusion also happen over just what the ...


2

The Biological Species Concept is largely useful in looking at the process of evolution. Since speciation isn't typically (though this isn't always true either!) an instantaneous process, it is useful to observe it in action. The BSC is the best way of approaching this (at least for sexually reproducing organisms). Back to your original question. It might ...


2

Bond and Oppell address your question points one, two and three empirically by looking for what they call "unbalanced bifurcations" as a sign of adaptive radiations in a well-resolved phylogenetic tree (spiders), and find that the number of unbalanced bifurcations does indeed exceed what they would expect to occur by chance. As you mention and as I ...


2

The fantastic number of species that one can observe today is not a fixed value. This number changes over time. These changes are not caused by De Novo origin of life but by two processes which are: exctinction Process by which a species disappear speciation Process by which one species (or one lineage) becomes two. Therefore the absolute change in ...


2

There is a really good discussion of this in Chesson & Kuang Nature 2008, they propose a way to measure niche complementarity accounting for competition and predation.


2

I am not sure I'm providing the kind of answer you would expect. Your question is very conceptual. For such question it is important to very well define the concepts you're using. For example, the concept of species is not well defined (and will certainly never be well defined as it does not represent a natural category to my point of view). Also, the ...


2

I think other answers have explained natural selection, but I think it is also important to note that species boundaries are applied in retrospect. This sounds blindingly obvious, but when presented by skulls from two species, such as Homo erectus and Homo sapiens, many will then ask where the evidence is for the species that came between those two. There ...


1

If all early forms of humans are gone, is it because the more modern humans had a greater evolutionary advantage? If you take an environment where species dwell, three things could have happened: The population got smaller and smaller, in a given environment, and then bam the last ones disappeared without producing any offspring. This is because ...


1

Could not fit in a comment… What kind of observations will you accept to be an observation? If we can demonstrate showing genetic data that two current species where actually only one some time in the past would it represent an observation to you? Or does it has to be a lab experiment (experimental evolution)? Experimental evolution with big animals take ...


1

By definition, polyploidy just means that a cell or organism contains more than 2 pairs of homologous chromosomes (or is more than 2n). This is more common in plants than it is in animals. The plant, as shown below, undergoes failed meiosis, which means that the diploid (2n) cells never become haploid (n). As a result, a plant ends up with more than 2n when ...


1

I've never heard of it, actually - though I can't speak for my professors or researchers I know, none have ever presented the Cladism argument as an argument for the delineation of species. As far as I'm aware, the attempts to define a species fall along three lines: The ability to produce fertile offspring in the wild. Distinct physical characteristics. ...



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